FIELD OF THE INVENTION
This invention relates to drilling heads and blowout preventors for oil and gas wells and more particularly, to a rotating blowout preventor mounted oil the wellhead or on primary blowout preventors bolted to the wellhead, to pressure-seal the interior of the well casing and permit forced circulation of drilling fluid through the well during drilling operations. The rotating blowout preventor of this invention includes a bowl which is designed to receive a blowout preventor bearing assembly and a swivel ball mounted in the bowl, to self-align the blowout preventor bearing assembly and swivel ball with respect to the bowl. A conventional drilling string is inserted or "stabbed" through the blowout preventor bearing assembly and swivel ball, which include at least two base stripper rubber units rotatably mounted in the blowout preventor bearing assembly and swivel ball to seal the drilling string. The device is designed such that chilled water may be circulated through certain pressure seals in the blowout preventor bearing assembly and liquid such as water may also be pumped directly into the bearing assembly between the stripper rubber seals, to hydraulically offset well pressure on the stripper rubber seals. Lubricant is introduced into stacked shaft bearings and also serves to offset well pressure exerted against key shaft pressure seals. The stripper rubber seals are attached to rotating mounting elements of the blowout preventor bearing assembly by means of clamp mechanisms.
Primary features of the rotating blowout preventor of this invention include the circulation of chilled water through the top seal box on the one hand, and pumping water or other liquid into the blowout preventor on the other hand, to both cool the pressure seals in the seal boxes and internally and hydraulically pressurize the spaced rotating stripper rubbers and facilitate offsetting higher well pressure on the stripper rubbers. A second primary feature is clamping of the respective stripper rubbers to the pot lid of the rotating top rubber pot and to the rotating shaft, respectively, to facilitate rapid assembly and disassembly. Another primary feature is swivel mounting of the blowout preventor bearing assembly on the fixed bowl to facilitate self-alignment of the blowout preventor bearing assembly with respect to the bowl and drilling string during drilling or other well operations. Still another important feature is lubrication of top and bottom bearings and offsetting well pressure on key shaft pressure seals by introducing lubricant into the bearing assembly. Another primary feature of the invention is the provision of a double split kelly driver design.
Oil, gas, water and geothermal wells are typically drilled with a drill bit connected to a hollow drill string which is inserted into a well casing cemented in the well bore. A drilling head is attached to the well casing, wellhead or to associated blowout preventor equipment, for the purposes of sealing the interior of the well casing from the surface and facilitating forced circulation of drilling fluid through the well while drilling. In the more commonly used forward circulation drilling technique, drilling fluid is pumped downwardly through the bore of the hollow drill string, out the bottom of the bore and then upwardly through the annulus defined by the drill string and the interior of the well casing and subsequently, from a side outlet above the well head. In reverse circulation, the drilling fluid is pumped directly through a side outlet, into the annulus between the drill string and the well casing and subsequently upwardly through the drill string bore and from the well.
Prior art drilling heads typically include a stationary body which carries a rotatable spindle operated by a kelly apparatus. One or more seals or packing elements, sometimes referred to as stripper packers or stripper rubbers, is carried by the spindle to seal the periphery of the kelly or the drive tube or sections of the drill pipe, whichever may be passing through the spindle, and thus confine the fluid pressure in the well casing to prevent the drilling fluid from escaping between the rotating spindle and the drilling string. As modern wells are drilled to ever deeper depths, greater temperature and pressures are encountered at the drilling head. These rigorous drilling conditions pose increased risks to rig personnel from accidental scalding, burns or contamination by steam, hot water and hot, caustic well fluids.